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Sideways Uni-Pivot Arm, SUPATRAC Blackbird, formerly "Ekos Killer (Price?)"

Discussion in 'audio' started by sonddek, Sep 20, 2020.

  1. yuckyamson

    yuckyamson pfm Member

    Is that him on the side? He looks like the one giving the demo, if anyone.
  2. sonddek

    sonddek Trade: SUPATRAC

    Yes, I think that's him. They all look very serious and attentive, as is right!

    My customer described the reproduction of this system as "very very amazing" and "ravishing". He also said that his SP-10 and Grado had sounded boring with previous tonearms. The rest of the system looks very interesting - but I'm out of my depth.
    effinity likes this.
  3. sonddek

    sonddek Trade: SUPATRAC

    I understand that Hyun Lee, the craftsman of Tedeska cartridges, wanted to hear one of his own cartridges on the Blackbird and installed it himself. The result was what my customer described as "very very amazing".

    Here is Tedeska's site:
    Darren L likes this.
  4. sonddek

    sonddek Trade: SUPATRAC

    I'm working very hard trying to catch up with orders after the delay of breaking my mitt. However, I finally broke a 12 inch arm during production and set it aside for chopping down to 11 inches for my Amadeus GT. It is looking and sounding great, possibly the best I've heard at home. Or anywhere, frankly.

    nmtjb, Tarzan, tiggers and 4 others like this.
  5. cromodora

    cromodora foshfishfie

    Hi Richard,
    I have PM’ed and emailed you since Monday about the Supatrac arm and have yet to receive a response.
    Please let me know if there is a problem with the shipment so that I can contact the courier.
    Thank you.
  6. sonddek

    sonddek Trade: SUPATRAC

    Hi cromodora,

    I did respond by email on Monday at 23.15 hrs BST. If you recall, last time we had delayed communications you found that your email client was filing my emails in your 'junk/spam' folder, so perhaps that has happened again. I will revert to private message now.

  7. sonddek

    sonddek Trade: SUPATRAC

    Now that all affected owners have been informed, I can report on two issues which have been raised by Adam at

    1) there have been two instances of rust affecting thrust boxes in humid climates. Each owner of a blackened steel thrust box will be receiving a replacement arm with a painted thrust box. I did not foresee this problem because I live in a fairly dry climate and none of my blackened steel thrust boxes, up to a year old, have been affected in this way.

    2) the new painted thrust boxes will also have compatibility with a zero underhang configuration, which, combined with a magnetic pivot, should eliminate marginal variations in azimuth experienced by some users. I was aware of this issue, and it is mentioned in the manual, but on my decks I consider it to be too small to worry about, and it does not seem to have any great effect on playback performance. To give some idea of the scale of this problem as I experience it, here are two images of azimuth on my Amadeus:

    Track 1

    Track 5

    I do not mean to belittle this issue, and I'm working on fixing it right now, but users who have discerned it report that they are enjoying excellent sound nonetheless.

    Under a microscope I have found that cartridge cantilevers invariably exhibit significant elasticity in response to torsion around their axes, so I consider that there is a degree or two of tolerance in what constitutes optimal lean. I also expect that it varies slightly from record to record because of the imperfect mastering process.

    My intended solution is to allow the hoist plane to be configured as vertical and to supplement pivot contact pressure using magnetism. My first two prototypes were of this kind before I began to see this as a marginal and probably inaudible issue, and the use of a magnet for the purpose of supplementing pressure on the pivot is specifically described in my patent application.

    Please don't hesitate to ask if you have any questions.
    Darren L likes this.
  8. yuckyamson

    yuckyamson pfm Member

    out of curiosity, can you summarize what the azimuth issue is in simple terms? As the cart travels inward towards the record center the arm tends to tilt....which way?
  9. sonddek

    sonddek Trade: SUPATRAC

    The variation is quite hard to see, as my photos above show, but when it is discernible the cartridge tilts very slightly towards the centre at track 1 and slightly away from the centre at track 5. In a well configured arm I believe that the amount is more or less negligible, but I would certainly prefer if this error never occurred and I take customer criticism very seriously.

    As far as I understand it, the reason for it is the hoist suspension underhang which means that the vertical axis for yaw movement is slightly tilted towards the cartridge, specifically at the equilibrium position. The natural arc of the cartridge is therefore on a circle which is slightly lower at track 3 than at tracks 1 or 5. This resolves as a very slight change in cartridge lean as the arm swings across the record. I emphasize that the effect is of a scale to be nearly invisible on my decks, and sonic performance remains unprecedented across the entire record.

    The solution is a vertical hoist plane so that the normal to the record is perfectly parallel to the yaw axis.
  10. yuckyamson

    yuckyamson pfm Member

    So if I have it right, because the Hoist assembly can only be exactly evenly hung (i.e. both the right hoist and the left hoist's threads have equal pressure applied to each side) at the center of the record's playable area (i.e. midway through the record), because ultimately the hoist is a thread that his hanging on a hook an the hook itself doesn't rotate left/right (which, if it would, would create another movable part), the hoist pulls somewhat torquing IN at the start of the record and, after the swivel has achieved equilibrium in the hoist at the middle, proceeds to pull and torque OUT as the hoist turns past equilibrium? Is that right?

    If that is the case I remember discussing with you. I thought the issue created would be SKATE or anti-skate, but I could understand if indeed it's actually create a YAW issue.

    Unless I'm way off base. Feel free to correct me.
  11. sq225917

    sq225917 Bit of this, bit of that

    Seems like sondek has a fix for it figured already.
  12. sonddek

    sonddek Trade: SUPATRAC

    I want to emphasize that the scale of this variation is such that under normal conditions on my own decks I can't see it. The photos above record this. I can't claim to be able to see any variation on that deck.

    However, I have noticed it more in the period after installation, which is why I think it can partly settle down with time.

    Theoretically, the quantity of deviation is dependent on the underhang, by which I mean the distance that the pivot point extends further from the post than the hoist suspension point. Underhang produces additional contact pressure at the pivot over and above the pressure produced by stylus drag and helps to stabilise the bearing contact. This dependency on underhang can be confirmed by setting excessive underhang so that the hoist plane is some way off the vertical, in which case azimuth deviation becomes more easily visible.

    When the arm's yaw axis is tilted forwards towards track 3, yaw across the record's flat surface will produce variation in azimuth. This is a geometric imperative which is true of all arms, and there are plenty of decks out there suffering from this minor misconfiguration.

    In the case of the Blackbird, tilting the yaw axis by a tiny amount is a design compromise the downside of which is insignificant compared to the audible tracking and rigidity gains of this bearing type, but since customers quite reasonably have concerns about it, I am introducing a small retrofit modification to eliminate the theoretical issue.

    BTW, I don't recommend this, but if you were to set up your turntable leaning a degree or two towards the front left corner, this alone would provide enough bearing contact to enable zero underhang, and the platter spindle and arm bearing yaw axis could then be perfectly parallel, eliminating this issue. Of course, theoretically your platter bearing is now compromised, but most decks are run like this and nobody seems to notice.

    All questions welcome.
  13. sonddek

    sonddek Trade: SUPATRAC

    This is exactly correct, but not the issue under discussion. Your point concerns residual skating forces in the bearing design. The Blackbird has an anti-skate mechanism which compensates for the bearing's residual skating forces when it is configured correctly. The anti-skate mechanism allows you to adjust both the difference between applied anti-skate force at the beginning and end of the record, and independently, the average anti-skating force. When you configure it correctly it will apply very little anti-skate force at the end of the record, since the bearing already applies some, whereas at the beginning it applies significantly more than would normally be required because it also needs to oppose the additional skating force residual in the bearing. For this reason I always test skating at the beginning and end of the record to ensure that both are in the good zone. Always remember that anti-skate force is never really right on any pivot arm because it is signal/drag dependent. Deviation in lean (azimuth) is a separate issue.

    I use 'yaw' to refer to the correct movement of a non-tangential arm across the record. The issue in question is lean (azimuth) deviation as the arm yaws in the required way. I hope that's clear. I know it can be difficult to discuss these things without animated diagrammes. 3D dynamics can be a bit mind-boggling.
  14. sonddek

    sonddek Trade: SUPATRAC

    Some of you may be aware that a significant number of people have built DIY versions of SUPAs, and invariably they report ground-breaking results. Here's a typical example from another place:


  15. yuckyamson

    yuckyamson pfm Member

    I think we are saying the same thing. For me YAW = AZIMUTH, i.e. that if the arm rotates ever so slightly on it's length-wise axis (as in, to restate, azimuth). So as the hoist is out of equilbirum (either being at the beginning of the record, or the end, essentially either side of midway through the record) the thread hoists, resting on a hook, which when the hoist threats wind around (this way or that, again away from center position), adds a bit of "tilt" to the arm, this way or that.

    Effectively the hoist hook is acting as a bearing of sorts. Richard obviously I'm not an engineer or designer, but it strikes me that this may very well be the compromise of the design and one worth living with. I'm not sure how you could fix this issue without creating another issue somewhere else or of some other nature. Let's say for example that the hoist-hook was itself allowed to would alleviate the YAW/Azimuth and skate/antiskate issue caused or influence added to those areas, but now you'd have a bearing, subject to noise, resistance, chatter, vibration, etc. So that's the point?

    It may be something to look at as your design develops but I'm just not sure how you'd work around it. The Underhung nature of the hoist is what puts forward pressure on the arm to push the thrustplate into the why ditch that? as you say when the stylus drags it helps the overall design concept as opposed to hurting it. How far out is the azimuth as of right now, at the extremes?
  16. sonddek

    sonddek Trade: SUPATRAC

    But that's not yaw. I don't think it helps to redefine well-established words as something else. The meaning of yaw is very clear in boats, aircraft and many other uses, so let's keep its traditional meaning with tonearms. The world is already enough like Alice's wonderland:
    There is no hook. The hoists convene at a 1mm diameter downwards facing hole.

    No, they don't.

    The issue before us is azimuth deviation due to the tilting of the bearing's yaw axis. It arises only because the arm is configured with a tilted axis. You can also configure it with a vertical axis in which case there is no azimuth deviation. Contact pressure at the bearing is easily supplied by magnetism instead of gravity, therefore underhang isn't necessary, the yaw axis can be vertical, and azimuth deviation is avoided. No yin-yang required.
    Chops54 likes this.
  17. yuckyamson

    yuckyamson pfm Member

    In order for the threads to "convene", the "downward facing hole" in effect acts as a hook. The bottom line is that as the hoist twists away from center there are some side effects.

    I am not, unfortunately, fully understanding the solution to the issue, perhaps not the issue at all. But I get from Adam's video that azimuth is off both at the entry of the record groove and at the end, in opposing directions. If you have a way to solve it without compromise, hats off. Would love to understand it more.
  18. sq225917

    sq225917 Bit of this, bit of that

    Vertical hoist. He has the answer already
  19. sonddek

    sonddek Trade: SUPATRAC

    I understand - it's not obvious how it works. That may be why it hasn't been done before. I don't find it easy to visualise or explain and I came up with the bloody thing. You are right that there are side-effects of the bearing, the most important of which is the need for a mechanism which provides variable anti-skate force.
  20. yuckyamson

    yuckyamson pfm Member

    So you think you can solve the azimuth issue without creating averse effects?
    Last edited: Oct 24, 2021

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